A64: Relax the register constraints for LSeqStringGetChar.

src/a64/lithium-codegen-a64.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 4625 matching lines @@
                                            LOperand* index,
                                            String::Encoding encoding) {
   if (index->IsConstantOperand()) {
     int offset = ToInteger32(LConstantOperand::cast(index));
     if (encoding == String::TWO_BYTE_ENCODING) {
       offset *= kUC16Size;
     }
     STATIC_ASSERT(kCharSize == 1);
     return FieldMemOperand(string, SeqString::kHeaderSize + offset);
   }
-  ASSERT(!temp.is(string));
-  ASSERT(!temp.is(ToRegister(index)));
+
   if (encoding == String::ONE_BYTE_ENCODING) {
     __ Add(temp, string, Operand(ToRegister32(index), SXTW));
   } else {
     STATIC_ASSERT(kUC16Size == 2);
     __ Add(temp, string, Operand(ToRegister32(index), SXTW, 1));
   }
   return FieldMemOperand(temp, SeqString::kHeaderSize);
 }
 
 
 void LCodeGen::DoSeqStringGetChar(LSeqStringGetChar* instr) {
   String::Encoding encoding = instr->hydrogen()->encoding();
   Register string = ToRegister(instr->string());
   Register result = ToRegister(instr->result());
   Register temp = ToRegister(instr->temp());
 
   if (FLAG_debug_code) {
-    __ Ldr(temp, FieldMemOperand(string, HeapObject::kMapOffset));
-    __ Ldrb(temp, FieldMemOperand(temp, Map::kInstanceTypeOffset));
+    // Even though this lithium instruction comes with a temp register, we
+    // can't use it here because we want to use "AtStart" constraints on the
+    // inputs and the debug code here needs a scratch register.
+    UseScratchRegisterScope temps(masm());
+    Register dbg_temp = temps.AcquireX();
 
-    __ And(temp, temp,
+    __ Ldr(dbg_temp, FieldMemOperand(string, HeapObject::kMapOffset));
+    __ Ldrb(dbg_temp, FieldMemOperand(dbg_temp, Map::kInstanceTypeOffset));
+
+    __ And(dbg_temp, dbg_temp,
            Operand(kStringRepresentationMask | kStringEncodingMask));
     static const uint32_t one_byte_seq_type = kSeqStringTag | kOneByteStringTag;
     static const uint32_t two_byte_seq_type = kSeqStringTag | kTwoByteStringTag;
-    __ Cmp(temp, Operand(encoding == String::ONE_BYTE_ENCODING
-                         ? one_byte_seq_type : two_byte_seq_type));
+    __ Cmp(dbg_temp, Operand(encoding == String::ONE_BYTE_ENCODING
+                             ? one_byte_seq_type : two_byte_seq_type));
     __ Check(eq, kUnexpectedStringType);
   }
 
   MemOperand operand =
       BuildSeqStringOperand(string, temp, instr->index(), encoding);
   if (encoding == String::ONE_BYTE_ENCODING) {
     __ Ldrb(result, operand);
   } else {
     __ Ldrh(result, operand);
   }
@@ skipping 1148 matching lines @@
   __ Bind(&out_of_object);
   __ Ldr(result, FieldMemOperand(object, JSObject::kPropertiesOffset));
   // Index is equal to negated out of object property index plus 1.
   __ Sub(result, result, Operand::UntagSmiAndScale(index, kPointerSizeLog2));
   __ Ldr(result, FieldMemOperand(result,
                                  FixedArray::kHeaderSize - kPointerSize));
   __ Bind(&done);
 }
 
 } }  // namespace v8::internal